Paul, W9AC, is correct that many of the broadcast rigs in the US that
use(d) air-cooled power tubes with handles and thoriated tungsten
filaments have/had a rheostat to adjust it. If the rheostat is
properly rated and not enclosed in a tiny chassis to overheat, it
should do an excellent job. An occassional touch up of the setting is
good to keep the wiper contact clean. Variacs, powerstats, are
useful, but they too have a wiper that needs to be moved once in a
while.
Use of a current limited transformer is also used in many rigs,
designed for a factor of 2 overcurrent. This takes care of the cold
turnon transient current per the tube manufacturers specifications.
Some systems also use a slow ramp up system to do this, and a
conventional transformer.
John
K5PRO
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